Surface mounted dielectric chip antennas are electrically small antennas often used on small platforms such as mobile communications devices. They are characterised by having a block of dielectric material mounted on a non-ground area of a circuit board. Conductive tracks are printed on the dielectric block and it is these tracks that form the antenna rather than the dielectric material itself.
Generally the dielectric chip antenna has a shape that is cuboid or a similar form of hexahedron, although other shapes are possible. A surface mounted chip antenna is generally characterised by having at least two conductive electrodes and often three; a feed electrode, a ground electrode and a radiation section. Sometimes monopole designs are used in which case there is no ground electrode; in this case additional solder pads, having no electrical functionality, may be used to add mechanical stability to the surface mounting process.
The antenna dielectric block material may be ceramic, resin or similar other dielectric material. The function of this dielectric block is to add mechanical support to the antenna and to reduce the antenna size. High dielectric ceramic materials (relative permittivity of 20 or greater) are often chosen, although this is not always the case.
Perhaps the simplest form of dielectric chip antenna is that described by EP 0766341 [Murata]. This discloses a quarter wave monopole printed on a dielectric block and fed capacitively across a small gap separating the feed electrode and the main radiating section of the antenna.
A more typical surface mounted dielectric chip antenna is disclosed in EP1482592 [Sony]. The antenna has feed and ground electrodes with a radiating section between the two. The resonant frequency of the antenna is determined by the pattern printed on the mounting board and not on the antenna itself. In this way the chip design does not need customisation for each application and the antenna is said to be standardised. The feed section printed on the mounting board is characterised as capacitive in nature because conductive plates on opposing sides of the mounting board are employed. In contrast, the grounded section printed on the mounting board is characterised as inductive in nature because of a narrow conductive strip that forms part of the design. By adjusting the form of these capacitive and inductive sections printed on the mounting board, the resonant frequency of the antenna may be adjusted without recourse to re-designing the dielectric chip itself. A variety of dielectric chip shapes are disclosed in EP1482592.
US 2003/0048225 [Samsung] discloses a surface mounted chip antenna having a dielectric block and separate feed, ground and radiation electrodes. The use of conductive patterns on the side surfaces of the dielectric block is disclosed as a means of lowering the resonant frequency and a T-shape is proposed for the feed section so as to aid matching. The dielectric block may have a hole in it to reduce weight and cost. The antenna is essentially capacitive in nature because of the capacitance between the feed and the ground electrode and the feed and the radiating electrode.
A broadband chip antenna is disclosed in US 2003/0222827 [Samsung]. Here a dielectric block has conductive electrodes disposed on two opposing end walls and parts of the top and bottom surfaces. One electrode is grounded, the other is a feeding element and the slot between the two electrodes gives rise to broadband RF radiation. No other information is given concerning feeding and grounding tracks as the antenna radiating element is considered to be the dielectric block and the electrodes disposed on it.
WO 2006/000631 [Pulse] discloses a similar arrangement of dielectric block metallization as US 2003/0222827. However, in this case the feeding and grounding arrangements on the circuit board are disclosed. One electrode is grounded (this is described as being a parasitic antenna) and the other electrode is connected to both the feed in one place and to ground in another, similar to the way a PIFA is fed. The width of the slot between the electrodes is used for tuning and matching. A ceramic material of relative permittivity 20 is used for the dielectric block material in the examples given.
WO 2010/004084 [Pulse] discloses metallization of a dielectric block so as to form a loop round the block. Generally the feed point is in one corner, but feeding half way along the dielectric block is also shown. A relative permittivity for the dielectric block of 35 is suggested.
EP 1003240 [Murata] discloses a similar arrangement of metallization, feeding and slot between electrodes to those shown in US 2003/0222827 and WO 2006/000631.
A slot diagonal to the sides of the dielectric block is proposed and the slot width varies along its length.
US 2009/0303144 discloses a dielectric chip antenna fed capacitively across a gap at one end and grounded at the other end so as to form a loop antenna arrangement. The feeding and grounding arrangements on the circuit board are disclosed and show a matching component on the feeding side and a frequency adjusting element (generally a capacitor or inductor) and the grounded side.
A further loop antenna arrangement is disclosed by US 2010/0007575. Here a loop is formed around the dielectric block and includes capacitive coupling between the upper and lower layers so as to complete the loop. The method of feeding is not shown in the figures but is said to be at one end of the block.
Most of the dielectric chip antennas described above are not stable against detuning, such as hand detuning when the antenna is deployed on a mobile device. Moreover, because the grounding arrangements of many of these chip antennas are crucial to their performance, the antenna performance is determined to some extent by the size and shape of the mounting board and the grounded area thereon. For example, a chip antenna may work well in the middle of one edge of the mounting board but not work well in one corner, or vice versa. It would therefore be desirable to provide an antenna having the advantage of the small size and cost of chip antennas but without the detuning and mounting sensitivities.
The present Applicant has explored the use of magnetic dipole antennas for mobile communications platforms in co-pending UK patent applications GB 0912368.8 and GB 0914280.3.